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Behavior of Antimony(V) during the Transformation of Ferrihydrite and Its Environmental Implications

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journal contribution
posted on 03.09.2013, 00:00 by Satoshi Mitsunobu, Chihiro Muramatsu, Katsuaki Watanabe, Masahiro Sakata
In this study, we investigated the behavior of Sb­(V) during the transformation of poorly crystalline Fe­(III) oxyhydroxides (two-line ferrihydrite) with various Sb/Fe molar ratios at pH 6.0. Both XRD and Fe EXAFS analyses confirmed that goethite and hematite are the primary transformation products of the ferrihydrite in the presence of Sb­(V). The crystallization kinetics showed that the transformation rate with Sb­(V) was approximately the same as that of the control (without Sb­(V)), which indicates that the presence of Sb­(V) does not influence the transformation rate to a noticeable extent. Throughout the transformation, Sb­(V) dominantly partitioned in the solid phase and no desorption of Sb­(V) was observed. Furthermore, Sb EXAFS analyses suggested that Sb­(V) in the solid phase is structurally incorporated into crystalline goethite and/or hematite generated by the ferrihydrite transformation. Hence, Sb­(V) transfers into the thermodynamically stable solids from the metastable ferrihydrite with aging, indicating a rigid immobilization of Sb­(V). These findings are valuable for making predictions on the long-term fate of Sb associated with ferrihydrite in natural environments.